This article is co-published with ProPublica, a non-profit newsroom that investigates abuses of power.

New advances in environmental science are providing a detailed understanding of the human cost of the Trump administration’s approach to climate.

Increasing temperatures are already killing enormous numbers of people. A ProPublica and Guardian analysis that draws on sophisticated modeling by independent researchers found that Donald Trump’s “America First” agenda of expanding fossil fuels and decimating efforts to reduce emissions will add substantially to that toll, with the vast majority of deaths occurring outside the US.

Most of the people expected to die from soaring temperatures in the coming decades live in poor, hot countries in Africa and South Asia, according to recent research. Many of these countries emitted relatively little of the pollution that causes climate crisis – and are least prepared to cope with the increasing heat.

ProPublica and the Guardian’s analysis shows that extra greenhouse gases released in the next decade as a result of the president’s policies are expected to lead to as many as 1.3 million more temperature-related deaths worldwide as the earth heats in the 80 years after 2035. The actual number of people who die from heat will be much higher, but a warming planet will also result in fewer deaths from cold.

Leaders from most of the countries in the world are now gathered at an international conference in Belém, Brazil, to address the escalating effects of the climate crisis. The absence of the US, which has 4% of the world’s population, but has produced 20% of its greenhouse gases, has been pointedly noted by participants. Afghanistan, Myanmar and San Marino are the only other nations that did not send a delegation to the meeting, according to a provisional list of participants.

Our calculations use modeled estimates of the additional emissions that will be released as a result of Trump’s policies as well as a peer-reviewed metric for what is known as the mortality cost of carbon. That metric, which builds on Nobel prize-winning science that has informed federal policy for more than a decade, predicts the number of temperature-related deaths from additional emissions. The estimate reflects deaths from heat-related causes, such as heat stroke and the exacerbation of existing illnesses, minus lives saved by reduced exposure to cold. It does not include the massive number of deaths expected from the broader effects of the climate crisis, such as droughts, floods, wars, vector-borne diseases, hurricanes, wildfires and reduced crop yields.

The numbers, while large, are just a fraction of the estimated 83 million temperature-related deaths that could result from all human-caused emissions over the same period if climate-heating pollution is not curtailed. But they speak to the human cost of prioritizing US corporate interests over the lives of people around the globe.

“The sheer numbers are horrifying,” said Ife Kilimanjaro, executive director of the non-profit USClimate Action Network, which works with groups around the world to combat the climate crisis.

“But for us they’re more than numbers,” she added. “These are people with lives, with families, with hopes and dreams. They are people like us, even if they happen to live in a different part of the world.”

The Trump administration, sometimes with the help of congressional Republicans, has dramatically set back efforts to limit the climate crisis – cutting tax credits for clean electricity, fuels, vehicles and manufacturing, easing pollution restrictions on coal-fired power plants and making it easier to drill on federal lands, to name just a few of the climate initiatives that wererecently reversed.

“Prior to Trump, we had the most ambitious climate policy that the US has ever come up with – our best effort to date by far of addressing this growing problem,” said Marshall Burke, an economist at the Doerr School of Sustainability at Stanford University.

“When we roll these things back, it is fundamentally affecting the damages we’re going to see around the world,” said Burke.

Responding to questions about the reversals and their projected consequences, White House spokesperson Taylor Rogers attacked what she referred to as the “Green Energy Scam”. “America still doesn’t buy the left’s bogus climate claims,” she wrote, without specifically addressing the forecast of heat-related deaths.

The finding that fossil fuels were causing the world to warm first made it to the White House least 60 years ago, when advisers to Lyndon Johnson warned that runaway emissions would lead to precisely the extreme events and rapid warming the planet is undergoing today. Scores of scientists have denounced the administration’s attitude toward the climate, noting there is overwhelming evidence that human-driven climate crisis is already causing damage that will only get worse.

When heat becomes deadly

The people most likely to die from rising temperatures are those already disproportionately vulnerable to extreme heat: laborers toiling outdoors, elderly people, the very young, who lose fluids especially quickly, people with disabilities and illnesses and people who lack air conditioning and stable housing.

Extremely high temperatures kill by overwhelming the body’s ability to cool itself. Sweating often ceases. Unconsciousness, organ failure and death follow. Rising temperatures also exacerbate existing health conditions, triggering heart attacks, strokes and respiratory problems that hasten death.

In recent years, the climate crisis has caused the number of deaths from heat exposure to climb around the world. In the US, deaths linked to heat have increased more than 50% since 2000, according to a recent study from the Yale School of Public Health.

Hundreds of people died in the Pacific north-west in 2021, when a high pressure system trapped hot air above parts of the area and caused temperatures to soar well above 100F (37.7C). Many of the older victims were found alone in their homes, without air conditioning or fans. One farm worker collapsed in a field, another in a nursery. A 65-year-old took her last breath in her parked car, essentially baked by the sun. A team of climate scientists found that the heat wave would have been virtually impossible without human-induced climate change.

Still, when deaths from both heat and cold are considered together, the total number of temperature-related deaths may not appear catastrophic right away. As the planet heats in the next few decades, the global decline in people dying from cold may almost entirely offset deaths from heat. But in the second half of the century, long after Trump has left office, the number of heat-related deaths is expected to greatly outpace the reduction of deaths from cold.

While the US has emitted more climate-heating pollution than any other country, when deaths from both heat and cold are considered together, it is expected to suffer only up to 1% of temperature-related deaths worldwide caused by the additional carbon emissions, according to a working paper by R Daniel Bressler, an assistant economics professor at Bentley University who developed the concept of the mortality cost of carbon.

Some of the world’s poorest countries will almost certainly struggle to adapt. Niger and Somalia – whose emissions are dwarfed by those of the US– are projected to have the world’s highest per capita death rates from increasing temperatures, Bressler found. India is expected to suffer more temperature-related deaths than any other country. Pakistan, which has just 3% of the world’s population, is expected to have between 6% and 7% of the world’s temperature-related deaths, depending on its ability to adapt to the effects of heat.

“People in my community will die,” said Ayisha Siddiqa, a Los Angeles-based climate activist whose family continues to live in her native Pakistan.

Siddiqa, who co-founded the environmental group Future Generations Tribunal, recalled the effect of heat on her family in 2022, when temperatures in Pakistan and India soared above 120F (48C). Like most people in the region, the Siddiqas do not have air conditioning. Her father, she said, lost consciousness and had to be hospitalized during the deadly heatwave.

“It’s unexplainable,” she said of the heat. “It’s kind of like the entire air around you is sticking to your body and you can’t breathe.”

Progress reversed

At this time last year, the US was on track to drastically reduce its emissions.

Under Joe Biden, the nation made landmark investments to turn away from fossil fuels, the primary driver of the climate crisis, and harness power from the wind and the sun. Hundreds of billions of dollars were being directed toward reducing emissions through a variety of initiatives, such as putting more electric vehicles on the roads and making office buildings and homes more energy efficient.

Biden also reversed Trump’s first-term decision to pull the US out of the Paris agreement, the international deal struck a decade ago in which countries pledged to work together to limit global heating.

But as soon as he returned to the White House, Trump began to undo it all. On his first day back, in front of a crowd of cheering supporters wearing Maga hats, he authorized the US to again pull out of the Paris agreement, which he had previously deemed a “rip-off”. Just 10 days earlier, the World Meteorological Organization had declared 2024 the hottest year on record.

Over the next 100 days, Trump instigated more efforts to roll back climate policies than he had in his entire previous term.

In March, his Environmental Protection Agency celebrated the “biggest deregulatory action in US history”, when it announced a slew of actions intended to reverse his predecessor’s efforts to rein in the climate crisis. Among them were regulations that restrict emissions from cars and trucks, limit air pollution from oil and gas operations and require power plants to capture planet-heating greenhouse gas emissions.

Then came the “big beautiful bill”, Trump’s nickname for the domestic policy mega bill he signed in July. The act cut tax incentives for solar and wind energy and electric vehicles, makes it easier and cheaper to drill or mine on federal lands, reverses efforts to cut emissions of methane, another greenhouse gas and increases government support for coal.

Calculating the lives lost

To understand the consequences of these moves, ProPublica and the Guardian used the results of modeling from Rhodium Group, an independent, nonpartisan research firm that analyzed the policy changes from this year. The group came up with a high, low and midrange estimate of the amount of additional emissions expected to be released in the next 10 years as a result of the rollbacks the EPA announced in March and the bill passed this summer. (The modeling also reflects changes to market forces and other factors.)

For our calculation, our starting point was Rhodium Group’s midrange number: 5.7bn metric tons of carbon through 2035. Using the firm’s other estimates would result in between 571,000 and nearly 2.2 million extra temperature-related deaths due to Trump’s policy changes. The Princeton University-led Repeat Project conducted a similar analysis and came up with 6.9bn metric tons, which would result in even more projected deaths.

To translate those emissions to deaths, ProPublica and the Guardian turned to the field of climate economics, which links human-generated emissions to measurable economic costs. A model that calculates what’s known as the social cost of carbon by Nobel laureate William Nordhaus has been used in federal policy since 2009, guiding everything from requirements mandated by the Securities and Exchange Commission to EPA regulations.

While Nordhaus estimated the broad economic cost of the climate crisis, Bressler, the Bentley University professor, used his model to focus just temperature-related death. Drawing also on public health research, Bressler estimated the amount of carbon expected to cause one death over 80 years: 4,434 metric tons. The figure is equivalent to the average lifetime emissions of 3.5 Americans or 146.2 Nigerians. Using the same estimate, Bressler also calculated how many deaths are expected over the course of 80 years from each additional metric ton of carbon released into the atmosphere. He published his findings in Nature Communications in 2021.

In response to questions for this story, the EPA, which recently stopped considering the social cost of carbon at Trump’s direction, rejected Bressler’s scientific analysis. The agency called it “an exercise in moral posturing, not rigorous science” and said that the calculation of deaths per metric ton of carbon is “based on unvalidated extrapolations” and ignores “the dramatic uncertainties that dominate long-term climate projections”.

Climate scientists, however, said that the mortality cost of carbon is a valid metric. Peer reviewers for Bressler’s published research described his paper as “valuable and intuitive” and relevant for designing policy. After publishing the study, Bressler went on to serve as climate staff economist at the White House council of economic advisers from 2021-2022.

Others have emphasized that, because Bressler’s model focuses narrowly on the direct effects of temperature, the estimates it generates are vastly lower than the total death toll from the climate emergency. It also does not capture the serious but non-deadly effects of extreme heat, such as reduced productivity and increased misery.

Bressler acknowledges his work produces estimates and the true number of additional deaths due to greenhouse gas emissions will depend on several unknowable factors, including how quickly people adapt to changing temperatures and market forces. Critically, future presidents and other countries could also upend predictions by taking new steps to reduce emissions.

Bressler’s 2021 paper previewed multiple futures for the planet. Under what he calls the “pessimistic” scenario, global emissions wouldn’t level off until the end of the century. It was under this scenario that Bressler estimated that, by 2100, the climate crisis will have caused 83 million people to die of temperature-related deaths around the world. This is the scenario that would result in 1.3 million deaths by 2115 from the additional emissions released over the next 10 years as a result of Trump’s policies.

If global emissions were to drop to almost zero by 2050, the projected toll from temperature-related deaths would fall to 9 million by 2100. Even then, Trump’s policy changes this year alone would still result in an additional 613,000 deaths.

Experts agree that, while both of the scenarios Bressler lays out are possible, the most likely amount of emissions will fall between these two extremes. Still, Bressler said, the projections underscore what’s at stake.

“If you do things that add emissions, you cause deaths,” he said. “If you do things that reduce emissions, you save lives.”

Abrahm Lustgarten of ProPublica contributed reporting

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